全文获取类型
收费全文 | 5632篇 |
免费 | 5篇 |
国内免费 | 15篇 |
专业分类
航空 | 2608篇 |
航天技术 | 2131篇 |
综合类 | 15篇 |
航天 | 898篇 |
出版年
2021年 | 39篇 |
2018年 | 85篇 |
2017年 | 70篇 |
2016年 | 58篇 |
2015年 | 29篇 |
2014年 | 100篇 |
2013年 | 144篇 |
2012年 | 125篇 |
2011年 | 213篇 |
2010年 | 148篇 |
2009年 | 230篇 |
2008年 | 291篇 |
2007年 | 146篇 |
2006年 | 107篇 |
2005年 | 160篇 |
2004年 | 165篇 |
2003年 | 199篇 |
2002年 | 111篇 |
2001年 | 197篇 |
2000年 | 99篇 |
1999年 | 158篇 |
1998年 | 165篇 |
1997年 | 126篇 |
1996年 | 120篇 |
1995年 | 176篇 |
1994年 | 198篇 |
1993年 | 90篇 |
1992年 | 119篇 |
1991年 | 51篇 |
1990年 | 65篇 |
1989年 | 118篇 |
1988年 | 46篇 |
1987年 | 57篇 |
1986年 | 54篇 |
1985年 | 173篇 |
1984年 | 141篇 |
1983年 | 126篇 |
1982年 | 125篇 |
1981年 | 206篇 |
1980年 | 55篇 |
1979年 | 56篇 |
1978年 | 52篇 |
1977年 | 46篇 |
1976年 | 41篇 |
1975年 | 49篇 |
1974年 | 39篇 |
1973年 | 36篇 |
1972年 | 58篇 |
1970年 | 29篇 |
1969年 | 31篇 |
排序方式: 共有5652条查询结果,搜索用时 15 毫秒
861.
862.
F.R. Mosher J.T. Young 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(6):173-177
We have investigated the use of real and synthetic stereo satellite images and stereo graphics in applications such as cloud-tracked winds, severe storm cloud analysis, and general meteorological interpretation. We have concluded that a stereo meteorological presentation is possible and desirable in an operational environment. Synthetic stereo could be used immediately in cloud-tracked wind operations. The presentation allows one to appreciate the interrelations between cloud motions and cloud structures, especially in multi-layered situations. Reprocessing of FGGE tropical wind sets with a synthetic stereo presentation showed some improved yields of low-level vectors, a significant increase in mid-level vectors, and very little change in the high-level vectors. Severe local storm real-stereo presentations are possible operationally because the 15 minute RISOP operations of GOES-East allow simultaneous scanning of both geosynchronous satellites twice per hour. The real-stereo height measurements of overshooting turrets are an improvement over infrared heights and can be used to monitor the strength of the thunderstorm updraft. Synthetic stereo presentations of thunderstorm tops can be presented in a non-linear fashion which stretches out the cloud top features. The synthetic stereo presentation is easier for most people to see. We recommend the use of a hybrid system where the viewing is done on the synthetic stereo image and the quantitative measurements are done on the real-stereo pairs. 相似文献
863.
G. Ohring P. Clapp T.R. Heddinghaus A.F. Krueger 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(4):305-308
Cloudiness modulates the radiation budget at the top of the Earth-atmosphere system. For radiation balance studies, for climate diagnostic studies, and for climate modeling studies, it is important to know the sensitivity of both the outgoing longwave radiation and the net (absorbed solar minus outgoing longwave) radiation of the system to changes in cloudiness on a global basis. Based on a 45 month series of NOAA satellite scanning radiometer observations, estimates of the global distribution of these sensitivity parameters are obtained. 相似文献
864.
Registration by integral-square error correlation of one-dimensional discrete-time waveforms which are treated as random processes with specified autocorrelation functions is considered. An important design parameter for this class of problems is the probability of anomaly (a false dip in the correlation function) because it gives an indication of system immunity to gross registration errors. Explicit expressions for this parameter are not possible, so bounds and appoximations must be derived. Two upper bounds and an approximation for the probability of anomaly are derived here. The use of these expressions is illustrated by an example. The relative utility of these performance indicators is shown for the example by comparison with actual values of the probability of anomaly obtained by computer simulation. 相似文献
865.
An analytical method is developed for determining the basic RF link parameters that are required in a satellite system design. Certain simplifying assumptions are required and specific system elements are selected. Two different design criteria are considered; optimizing the per-beam signal energy to noise spectral density ratio (Eb/N0), and minimizing the per-user costs. These two criteria are complements of each other subject to coverage and performance constraints. The model can be used to rapidly assess tradeoffs in various system elements. A specific example of a domestic satellite system is considered. The economic analyses are also considered and the economy of scale effect is demonstrated for the design example and considered. 相似文献
866.
Experiments of prolonged bedrest in antiorthostatic position are conducted in order to simulated cardio-circulatory modifications observed in weightlessness. Until now, no studies of r.C.B.F. have been effected in these conditions. Six young, healthy volunteers (average age 23.8) were placed in strict bedrest and in antiorthostatic position -4 degrees for 7 days. The r.C.B.F. measurements were studied by 133Xe inhalation method using a 32 detectors system. Studies were made first in basal conditions, then between the 6th and 12th hr, and finally between the 72nd and the 78th hr after the beginning of the experiment. Three of the subjects received 0.450 mg of Clonidine daily during the experiment. In the subjects having taken no Clonidine, we observed a constant increase in r.C.B.F. (12, 17 and 16% respectively) in the first 12 hr; at the 72nd hour, all values had returned to basal state. This findings agrees with the well known notion of a rapid correction of hemodynamic disturbances observed in the first days of weightlessness. In the subjects treated with Clonidine, the increase of r.C.B.F. did not occur. Several mechanisms of action are possible; the Clonidine affecting either the heart by inhibiting volemic atrial receptors or the brain by direct vasoconstriction. 相似文献
867.
868.
Many simple radars use fact-risetime pulses, but wide bandwidth does not translate into corresponding high resolution since the spectrum is far from flat. A scheme for enhancing down- and cross-range resolution of multiple targets through a two-step partial equalization of the spectrum is illustrated by detailed computer simulation, with emphasis on the tradeoffs between resolution and signal-to-noise ratios. Three examples are treated: two equal scattering centers, two unequal scattering centers, and compound target 相似文献
869.
MARC (modeling, animation, rendering, and compositing), a system using advanced computer graphics and animation techniques for spacecraft mission simulation, is described. The MARC system provides capabilities for generating complex models of both man-made and natural phenomena. The system models orbital dynamics of terrestrial satellites, supports solid models for the Earth, Sun, and Moon, and simulates the dynamics of terrestrial satellites for arbitrary elliptical orbits. A stellar background including magnitudes and spectral types is generated. The elements of the MARC system, including object modeling tools, orbital animation techniques, the rendering system used to compute individual frames, and the compositing techniques used, are discussed. The software architecture of the MARC system and the hardware used to support the system are described 相似文献
870.
Severns J.G. Hobbs R.M. Elliott N.P. Towsley R.H. Conway R.W. Virshup G.F. 《Aerospace and Electronic Systems Magazine, IEEE》1989,4(12):8-12
The LIPS III satellite, which was launched into a 1100-km circular orbit of 60° inclination in the spring of 1987, is discussed. LIPS III is a member of the living-plume-shield class of spacecraft, all of which were built around a simple sheet metal plume deflector. The purpose of LIPS III was to provide a testbed for space power sources. An overview of the LIPS III system is given, and the experiments submitted for it, all but one of which were photovoltaic in nature, are described 相似文献